Information processing apparatus including a personal computer, which uses a variety of image display devices such as a Cathode Ray Tube (CRT) or an Liquid Crystal Display (LCD), have been adapted to output various kinds of image signals according to different manufacturers, types, etc. Therefore, as an image display device having a function that can accommodate these various kinds of image signals, a device so-called a multi-scanning type monitor has been developed recently.
The following will describe an image signal (video signal) input from a typical information processing apparatus to an image display device, with reference to FIGS. 14 and 15. FIG. 14 shows a waveform of the video signal in its one horizontal scanning period and FIG. 15, a signal waveform of the video signal in its one vertical scanning period.
As shown in FIG. 14, each of the horizontal scanning periods is defined by a horizontal synchronization signal SYNCH having a constant cycle. Each of the horizontal scanning periods is comprised of a pulse width interval of the horizontal synchronization signal SYNCH, a back porch interval BPH, a horizontal active interval ACTH, and a front porch interval FPH. In the horizontal active interval ACTH of these, an image is actually displayed horizontally on a screen, while the back porch interval BPH and the front porch interval FPH are displayed as black borders at right and left ends respectively on the screen.
Further, as shown in FIG. 15, each of the vertical scanning periods is defined by a vertical synchronization signal SYNCV having a constant cycle. Each of the vertical scanning periods is comprised of a pulse width interval of the vertical synchronization signal SYNCV, a back porch interval BPV, a vertical active interval ACTV, and a front porch interval FPV. In the vertical active interval ACTV of these, an image is actually displayed vertically on the screen, while the back porch interval BPV and the front porch interval FPV are displayed as black borders at top and bottom ends respectively on the screen.
As shown in FIGS. 14 and 15, an image signal has a few timing factors (hereinafter referred to as “timing data”), so that if even only one of them is different, the image signal is different in kind. For example, typically, image signals having different frequencies (horizontal synchronization frequencies) of the horizontal synchronization signals SYNCH generally have the different back porch intervals BPH, horizontal active intervals ACTH, or even front porch intervals FPH. This holds true also in the vertical direction.
Kinds of such image signals are different with the corresponding devices such as a computer or a video card from which the image signal is outputted, thus numbering a few hundreds of kinds conceivably. The multi-scanning type monitor described above is required to be capable of displaying any kind of an image signal input thereto on its screen with a right size at a right position. Therefore, to accommodate such a requirement, the following methods have been employed conventionally.
A first method is as follows. That is, beforehand, at a factory, an image signal having known timing data is actually input to an image display device and make an adjustment so that an image may be displayed with a predetermined size at a predetermined position on a screen of the device, and the adjustment value (adjustment parameter) of this condition is written into a nonvolatile memory etc. corresponding to a kind of the image signal. Such the processes for adjustment and adjustment-value write-in are performed for all known image signals that are expected to be used. In actual use, on the other hand, the kind of an image signal input from a computer of a user is checked, so that an adjustment parameter corresponding to the kind is read out of the nonvolatile memory and used for the display.
A second method is as follows. That is, in actual use, all items of timing data relative to an input image signal are measured, so that based on the timing data, predetermined arithmetic operations are performed to obtain an adjustment parameter, which is in turn used for the display. In this case, in contrast to the first method, it is not necessary to perform adjustment at the factory beforehand.
However, for the first method, at the factory, it is necessary to adjust a few adjustment parameters for each kind of image signal, so that if a few hundreds of kinds of image signals are to be accommodated, adjustment is necessary each time the image signal to be input is switched, thus consuming much time and labor, which is a problem. To solve this problem, such a method may also be thought of that, for example, a size and a position of a display region on a screen are detected by sensors and then subject to automatic adjustment so that they may be optimized. However, this method needs to provide an automatic adjusting machine, thus contributing to an increase in manufacturing cost.
Further, for the second method, all items of the timing data relative to an input image signal are measured, so that based on the measured value, an adjustment parameter is calculated, thus deteriorating an adjustment accuracy if an error occurs in measurement, which is a problem. In particular, if the image signal has a high frequency or a small active interval (e.g., in a case where the signal represents a dot or a line), a large error may possibly occur in measurement to deteriorate the adjustment accuracy significantly. Furthermore, it takes rather long time to measure the timing data relative to the image signal, thus prolonging a lapse of time from a moment when the image signal is input to a moment when a proper image appears on the screen, which is a problem.
To solve these problems, the present applicant has earlier proposed a method for first storing in storage means timing data relative to signal waveforms for each kind of an image signal, and, in actual use, detecting the kind of the input image signal to calculate an adjustment parameter using the timing data that corresponds to the kind of the image signal which has been stored in the storage means, thus displaying an image based on the adjustment parameter (see Japanese Patent Publication No. H11-52934). This method eliminates the problems of the first and second methods described above.
However, this method is adapted to store timing data that corresponds to a plurality of kinds of image signals and so requires a mass capacity memory, thus increasing costs of the device as a whole, which is a problem.
Further, this method of calculating an adjustment parameter using timing data that corresponds to a kind of an image signal in order to display an image based on the adjustment parameter has another problem that the image cannot be displayed at a right horizontal position if a deflection system is deteriorated over time.